This invention relates to gas turbine engines and particularly to the mounting of outlet guide vanes in the exhaust duct of such engines.
Outlet guide vanes of a gas turbine engine form an annular array positioned immediately to the rear of the turbine stage and are employed to straighten the flow of hot exhaust gas emanating from the combustion chambers and which have been swirled during their passage through the turbine. The vanes extend radially between the inner wall of the exhaust nozzle and the outer wall of the exhaust diffuser cone which is co-axial within the exhaust nozzle. The cone may move axially a small amount between a forward position when the engine is not running, and a rearward position when the engine is running due to the gas flow through the exhaust nozzle applying a rearwardly directed force upon the cone.
Due to the very high temperature of the exhaust gas it is necessary to manufacture outlet guide vanes from very specialized materials such as ceramic and, in one particular case, outlet guide vanes which comprise blades of aerofoil section with end plates are integrally moulded from a sleeve of a knitted ceramic. Such vanes are known as knitted vanes; they are structurally weak and, because they are secured to the engine structure at one end only so as to allow their unrestricted radial extension, their mounting arrangements are difficult to provide. Knitted ceramic vanes are discussed in the present applicant's published British Patent Specification 2,251,001A.
It is an object of the present invention to provide a means of mounting knitted vanes in an annular array which provides their freedom of radial extension, allows axial movement of the exhaust diffuser cone and enables the rearward load applied to the cone by the exhaust gas to be supported more evenly by all of the vanes in the array.